Intertherm Furnace Blower Wont Shut OFF

[Roger]

I have a Intertherm Furnace and the blower will not shut off. I put on a Honeywell programable thermostat about 3 months ago and everything was working fine. Last week the air conditioner turned on and the blower motor has not shut off since. I put the old thermostat back on and this did not fix the problem. I even left the thermostat completly off and the motor still ran. The status light on the circuit board blinks on and off at about 1 second intervals. I removed the limit switch from the top of the furnace by the blower and pressed on it and it shut the blower off. This to me seems backwards.

The model of the furnace is M3rl080A BW

[hvac1000]

((I removed the limit switch from the top of the furnace by the blower and pressed on it and it shut the blower off. This to me seems backwards. ))

Was there a red button in the center of the switch? Is that what you pushed? My system is wired so if the high limit makes the blower comes on and will not turn off till it is reset. I believe this is a safety circuit device. The high limit will also kill the power to the gas valve for further protection. Mine has activated in the summer when I am gone for a few day is hot weather. I guess the pilot lite and the high air temp in the home causes it to trip and when I arrive at the home a few days later my blower is running. When this first happened it took me awhile to figure it out and I have been in the HVAC business for years.

[Roger]

No there was not a red button on the top of the limit switch. The best way to describe it is it looks similar to a car thermostat and has two connections on top for wires. (look on this web site at gas parts and look at limit switches) What I pushed was the bottom which would be inside the furnace and I am guessing but when the metal on the bottom heats and cools it expands and turns the blower on and off. It seems to me that if I push in on the bottom, the fan should not turn off, but I dont know. I found on the inside of the door there are error codes posted. I did not notice them the first time, very small print, but it says that if it is continuous flash then it is a faulty flame sensor or the gas relay valve has shorted. Any opinions on this?

[hvac1000]

((I removed the limit switch from the top of the furnace by the blower and pressed on it and it shut the blower off))

The limit switch you pushed on is a safety that actually cuts off the voltage to the gas valve circuit. Or it could be a fan control. Usually if they are located in the top of the unit next to the blower they are a safety limit.

Pushing on this device should not make a difference unless it was stuck or defective. The only ones that can be pushed and make a difference are the limit controls like I mentioned before and they do have a red reset button.

If you diagnostic tool is telling you than the number of flashes is indicating a certain problem then I would believe that diagnosis and check out the components to see which is defective.